A known sprinkler of this type comprises a stationary guide cylinder which is connected to a primary and a secondary water-supply conduit and surrounds two telescopically interfitted riser tubes, i.e. a double-walled outer first-stage tube and an inner second-stage tube in which there is mounted a movable piston for remote control of the operation of the sprinkler.
The drawbacks of the known retractable two-stage sprinkler lie in the presence of axial bores in the pistons of both telescopic stages through which water flows out ineffectively when the tubes are raised above the ground surface, thus reducing considerably the lifting force of the pistons, as well as in the need for a movable piston with remote control in the second stage, which requires frequent resetting and reduces the operational reliability of the sprinkler.
In our copending application Ser. No. 029,476, filed Apr. 12, 1979, there has been disclosed a single-stage retractable spray head or sprinkler with a hollow piston whose axial bore is connected by means of radial holes to an annular groove in the external surface of the piston head, the upper part of the guide cylinder surrounding that piston having two sets of radial holes on different levels which are embraced from the outside by a ring chamber.